A basic conventional fluid filter operates by separating the solid contaminants from the fluid by utilizing a porous barrier that allows the fluid to pass and thereby contains the solid contaminants thus separating the particulate contaminants from the fluid. The most common barrier is a screen or mesh constructed of various materials that are compatible with the fluid characteristics such as fluid pressure, fluid temperature, and fluid corrosion issues. The typical fluid filter barrier has substantially symmetric openings that are sized such that they allow contaminants through that are sized smaller than the openings and that the barrier retains contaminants that are sized larger than the openings. Almost all of the typical particulate contaminants are approximately spherical in shape and if the overall size of the contaminants is larger than the barrier openings, the individual contaminant will partially wedge itself into the barrier opening from the force of the fluid flow through the barrier, if the individual contaminant is slightly larger than the barrier, however, if the individual contaminant is markedly larger than the barrier then the individual contaminant will most likely not wedge itself into the barrier. Thus, there are multiple points of contact between the barrier opening and the contaminant thus allowing the contaminant to become wedged into the opening, resulting in shorter filter lives as the more barrier openings that are substantially blocked by the contaminants result in the filter reducing its overall fluid flow rate ability for shortening the effective life of the filter as the filter loads up with contaminants.
If, for example a back flush operation is initiated, in other words reversing the fluid flow direction through the barrier in an effort to dislodge the contaminant that is wedged in the opening, the contaminant may not easily be dislodged due to the multiple points of contact with the opening with this being coupled with the usual semi resilient nature of the barrier (that is typically constructed of paper, or a polymer, wire mesh, and the like) and the contaminant (that can be fluid soaked, or resilient itself in a non symmetrical manner), resulting in retention of the individual contaminant in the barrier opening even during a back flush operation. In addition, the fluid flow force to dislodge the contaminant from the barrier is limited by the differential pressure capability of the barrier and the mechanical strength of the filtering material.
This drawback of the individual contaminant wedging into the barrier opening has been recognized in the prior art with one solution being to reshape the openings from substantially symmetric to a non symmetric shape that is typically a long thin rectangular opening that results in the individual contaminant having only two points of contact with the barrier opening which typically results in the individual contaminant being less “wedged” into the barrier, allowing in more effective removal of the individual contaminant from the barrier by the above described back flushing procedure as previously described, wherein this is typically termed a “self cleaning” fluid filter. Also, as an enhancement and at times a necessity structurally, the long thin rectangular opening in the self cleaning fluid filter barrier is constructed of a substantially rigid material (as compared to the conventional filter barrier being constructed of a typically resilient material as previously discussed) to accommodate the long span of the long thin rectangular opening which is a positive for further facilitating the dislodging of the contaminant from the barrier during the back flushing operation. Typically, self cleaning fluid filters have two different modes of operation, the first mode is to have three continuously operating filter fluid ports that include a dirty fluid inlet port, a clean fluid outlet port, and a dirty fluid outlet port, under this mode of operation the self cleaning fluid filter is continuously cleaned (with no back flushing required) and has an uninterrupted fluid filtering operation by essentially having a continuous flow of dirty fluid, wherein a continuous clean fluid flow is “bleed off” through the self cleaning filter, as this mode being the ideal for continuous self cleaning fluid filter operation being substantially maintenance free. When a fluid flow system cannot tolerate the continuous dirty fluid flow outlet (as in the case of for example, a fuel filter system or an oil filter lubrication system in an engine), in other words the fluid system requires a filter that has a single dirty fluid inlet and a single clean fluid outlet, (i.e. being a closed loop system as is typically required on a vehicle, boat, or any other mobile equipment) this is where a self cleaning filter would require an intermittent back flushing operation which is the second mode of a self cleaning filter operation. The second mode is to have two intermittently operating filter fluid ports that include the dirty fluid inlet port and the clean fluid outlet port, wherein an intermittent back flushing operation is required to remove an accumulation of trapped fluid contaminants from the filter by reversing the fluid flow such that the clean fluid outlet becomes the clean fluid inlet and the dirty fluid inlet becomes the dirty fluid outlet, with the back flush operation continuing until substantially all of the contaminants are removed from the filter.
Another type of self cleaning “filter” is called a centrifugal separator, wherein the fluid is spun in a vortex and through the use of centrifugal force the heavier particulates are spun outward against a typically frustroconically shaped wall (usually with the narrow end downward) to settle out of the spinning fluid downwardly and the clean fluid floats out of the vortex centrally upwardly with the larger heavier particles removed. The centrifugal separator works fluid flow wise much like the previously described first mode of operation for the self cleaning filter, wherein there is no backflushing required i.e. there is a dirty fluid inlet (typically tangentially located adjacent to the frustroconical wall), a dirty fluid outlet (typically located at the bottom of the narrowed frustroconical wall), and a clean fluid outlet (typically located at the top central portion of the frustroconical chamber), wherein proper operation of the centrifugal separator is maintained by proper pressure differences and flowrates maintained between the dirty fluid inlet, the dirty fluid outlet, and the clean fluid outlet. Thus, the centrifugal separator is a continuously operating and non maintenance device, which makes it seem attractive, however, it is not really a filter and is really more of a classifier to separate heavy particulates from the lighter fluid, thus the “filtration” is by no means absolute, i.e. light particulates would not be separated out and some heavy particulates could be included in the clean fluid outlet, thus for many applications a centrifugal separator would not be desirable. A further type of self cleaning filter is a type for use with gases to remove particulate matter from a gas stream either on a conventional filter material, or including a dielectric material in the filter by polarizing the dielectric material across a pair of electrodes to electrically collect particulates from the gas stream. Then making the filter self cleaning by vaporizing the collected particulates from either a conventional filter or dielectric filter using a higher electrical potential than is used to collect the particulates in the filtration process, thus the vaporized particulates are reduced in size to be acceptably passed through the filter. A yet further type of self cleaning filter is to mechanically “scrape” the filter element of contaminate build up as part of a built in self cleaning filter apparatus.
In looking at the prior art in this area, in U.S. Pat. No. 5,078,875 to Lösing disclosed is a separator for removing dirt and water from a liquid fuel that has a rectangular cross section central portion of its housing provided with a filter and a cup shaped lower portion of the housing having a guide tube through which the liquid is introduced downwardly around a vaned helical body generating a vortex flow of the liquid before it is diverted downwardly around the guide tube into the bowl chamber. The exterior of the guide tube is formed with a pair of horizontal V-shaped feedback passages which draw droplets of the liquid of higher density downwardly to meet the flow from the interior of the guide tube before it is deflected upwardly to the final filter, thereby increasing the separation efficiency.
Further, in U.S. Pat. No. 4,298,465 to Druffel disclosed a self-contained apparatus for the separation of low density fluids, such as fuel, from higher density fluids such as water and also other particles is disclosed which may be easily retrofitted into a variety of existing new and used engines as it can selectively accommodate the various fuel line arrangements and also various obstructions of these engines. Further, the apparatus includes improved flow director means which provides for the separation of the higher density fluid and the particles from the low density fluid at an earlier stage contributing to a more complete separation prior to the filtration of the fluid. Consequently, the filter element has an extended life due to the fact that it is exposed to less higher density fluids and particles in filtering the low density fluids.
Continuing in the prior art in U.S. Pat. No. 4,312,751 to Casamitjana disclosed is a device for separating contaminants from a liquid with which such contaminants are not miscible. Casamitjana comprises an inlet and outlet portion formed with an inlet opening for allowing liquid to enter the device and an outlet opening for allowing liquid to leave the device, and a separator portion, the separator portion being releasably secured to the inlet and outlet portion and including a generally cylindrical receptacle. The cylindrical receptacle in Casamitjana which in use, is disposed with its central axis substantially vertical and with the inlet and outlet portion of the device at its upper end, and an impeller element at the upper end of the cylindrical receptacle and disposed to receive liquid entering the device by way of said inlet opening and to conduct such liquid into the receptacle while imparting a rotational component of movement thereto. Whereby the contaminants in Casamitjana are separated from the liquid by centrifugal effects and settle to the bottom of the receptacle while liquid having contaminants separated therefrom leaves the device by way of the outlet opening. Wherein the stilling vanes 9 in Casamitjana act to keep the particles and heavier fluids at the bottom of the bowl, also the inverted cone 10 helps to drive the particles and the heavier fluid toward the bottom of the bowl also.
Next, in the prior art in U.S. Pat. No. 4,456,529 to Shinaver disclosed is a filter apparatus for separating fluids of different densities. The apparatus has a relatively small housing size such that it is particularly suited for installation in passenger vehicles. The construction of the subject filter in Shinaver is intended to eliminate sealing problems found in the prior art as well as to permit the utilization of a filter having increased capacity by virtue of it being a cylindrical filter.
Further, in the prior art in U.S. Pat. No. 4,502,954 to Druffel, disclosed is a combination fuel filter and water separator which is particularly useful at the upstream, suction side of a fuel pump that includes a provision for initial settling of water and particulate material in a lower chamber, after which the fluid passes up through a backflow preventing check valve and into an upper chamber, where fine filtration takes place. In Druffel, the check valve, preferably a ball valve between the lower and upper chambers, prevents any backflow of fuel by gravity from the filter/separator assembly when a top cover is opened, e.g. for servicing of a filter element in the upper chamber. The location of the ball valve in Druffel avoids subjecting it to highly contaminated entering fuel, which could foul the valve. Associated with the inlet structure of Druffel the assembly is a channel for inducing a helical flow path for centrifugally removing water and particles while imparting a downward component of motion to them, noting that this is similar in construction to Shinaver.
Self cleaning or substantially self cleaning filters are in general highly desirable due to lower maintenance required, reducing periodic or inadvertent shutdowns of a fluid process or system i.e. by almost having completely continuous use, and are “greener” environmentally in that there is reduced disposable waste generated from used or contaminated filter elements, of which can be an environmental problem if the filtered fluid is toxic, flammable, and the like. What is needed therefore is a substantially self cleaning filter having an expanded micro filtering ability due to combining multiple filtering processes of centrifugal particulate separation, multiple stages of straining, and a final fine filtration to provide micro filtration with the longest filter assembly life before needing maintenance. This as opposed to the conventional single stage non self cleaning filter wherein all of the filter fluid flow force tends to hold the contaminates trapped into the filter element, thus further entrapping and wedging the contaminates into the filter element wherein the buildup of these contaminates occurs at a faster rate necessitating more frequent filter maintenance.
It is desired that the present invention of a self cleaning filter, have the ability to filter down to a very fine level of about 10 micron absolute, while being able to centrifugally remove heavier fluids and particles upstream of the final 10 micron absolute filter along with successive stages of finer particulate straining also removing particulates upstream of the final 10 micron absolute filter to maximize the intervals between filter maintenance in a closed loop system wherein a continuous dirty fluid outlet cannot be tolerated that a true self cleaning filter requires.